The present invention relates to an inking plate for a rotary printing machine, the plate being designed to be mounted on a cylinder, and being formed of at least a base plate and material deposited on the plate, the material being designed to be cut in relief areas which define the surfaces to be inked. The present invention also relates to a printing machine comprising such a printing plate mounted on a cylinder and a method for producing such a plate.
These inking plates mounted on inking cylinders are known in the case of rotary printing machines, both for direct and indirect printing. In the case of indirect inking, the necessary ink is transferred to an inking/collecting cylinder from separation cylinders, also known as inking cylinders. Each of these inking cylinders is associated with a particular ink duct and consequently with a given color. The collecting cylinder then transfers the ink corresponding to the various colors to the printing plates. In the case of direct inking, on the other hand, the ink is transferred to the printing plates directly from the inking cylinders, without using a collecting cylinder.
The inking cylinders, in a manner known in the prior art, have a surface made of a hard material, e.g. plastic, metal or hardened rubber, this surface being cut in such a way as to form relief areas whose limits define the areas to be printed in a given color. These relief areas are formed by known cutting means, such as laser.
Such inking rollers are described for example in European patent application EP 0 406 157 and in U.S. Pat. No. 5,282,417 which shows such inking rollers mounted on a printing machine using both direct and indirect printing techniques.
This type of inking cylinder nonetheless has disadvantages. In particular, once they become worn, that is when the relief areas are worn down, it is necessary to remove the cylinders from the printing machine, redeposit a layer of plastic or other material on its circumference, re-cut the desired relief areas and finally refit the cylinders in the machine, which requires time-consuming and complicated adjustments to reestablish correct registration of the different impressions on the collecting/inking cylinder or on the plate cylinder.
One way of overcoming some of these disadvantages is to use inking plates with a photopolymeric coating which are then mounted on cylinders replacing the known inking cylinders. These plates can therefore be prepared independently, notably by forming the relief areas by a photogravure process, but these photopolymeric plates have disadvantages of their own. In the first place there is the fact that the relief areas have to be generated flat, which means that these relief areas are deformed when the plates are mounted on the cylinder. It is therefore essential to take account of this deformation while generating the relief areas. In addition, the diameter of the cylinders on which the plates will be mounted also has an influence on the deformation. Besides their cost, these photopolymeric plates also have a short life. In fact, particularly in processes that use the principle of direct inking of the printing plate, the temperature of which may be high, photopolymeric plates have a much shorter life than the inking cylinders mentioned above. Furthermore, the photopolymeric material has poorer elasticity than the materials used for inking cylinders and inking is therefore sometimes inadequate, especially in a direct-inking process.
It is an object of the invention to improve the known inking systems.
More particularly, it is an object of the invention to propose an inking plate that overcomes the problems of known plates.
It is also an object of the invention to propose a process for producing such an inking plate, an inking cylinder carrying such an inking plate and a rotary printing machine using such an inking plate.
The inking plate according to the invention is defined by the cutting of the reliefs in a hard deposited material occurring when the base plate (11) is held in a rounded condition so as to permit mounting on the cylinder after cutting without substantial elastic deformation of the base plate (11) or the deposited material from its as-cut state.
There are many advantages to the plate according to the invention. In the first place there is the fact that such plates are much less expensive to produce and they last much longer than photopolymeric plates. In addition, they are much simpler to manufacture because the relief areas are generated on plates mounted on cylinders, so that these areas are not deformed when the plates are installed in a printing machine.
In further embodiments, the inking cylinder for a printing machine comprising at least one printing plate according to the invention.
In another embodiment, a process for producing a plate according to the invention is provided.